This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 1. Confirm the unique profile of plasma angiogenic growth factors in sickle cell disease and determine its impact on EPC migration, tube formation and lineage commitment. 2. Determine whether migration and vascular tube formation of EPCs derived from subjects with sickle cell anemia is innately abnormal. 3. Examine the commitment of EPCs from subjects with sickle cell anemia towards the endothelial and smooth muscle cell lineages. 4. Define patterns of arterial stiffness in healthy controls and children with sickle cell anemia, and their relationship to EPC number, function, and angiogenic growth factor levels.